Some say that you got a mentor for a restricted time you finished the adept/mentor relationship and then the contact stop. If you got a good relation with your mentor, the relation don`t stop.
For some time ago I talked to an adept in the very first mentor program I coordinate in 2000/2001 as a project within an organization called Junior Chamber International (www.jci.cc) and she still got contact with her mentor after 8 years.
This was a mentor program JCI offered for young people within Young Enterprise (www.ja-ye.org) in Norway (www.ue.no) and she was 16 years old.
So she had contact with the mentor from 16 to 24, so this was a really good job from the mentor. And the adept really understand what mentoring could do for here in a period in life where there is a lot happening.